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Dynamics of children's gait
Human Movement North-Holland
Science 8 (1989) 465-480
DYNAMICS
OF CHILDREN’S
Nancy
L. GREER
University of Minnesota,
GAIT
* Mwmeapolis,
Joseph
HAMILL
University
of Massachusetts,
Amherst,
USA
USA
Kevin R. CAMPBELL Cleveland Clinic Foundation,
USA
Greer, N.L., J. Hamill and K.R. Campbell, 1989. Dynamics gait. Human Movement Science 8, 465-480.
of children’s
The purpose of the present study was to examine the characteristics of gait in 3- and 4-year-old children. Eighteen children completed 20 walking passes on each of two days. Sagittal plane kinematics and ground reaction force patterns were analyzed. From the kinematic data, high standard deviation values were noted for many of the segmental and angular velocity variables, especially the more distal segments and joints. Differences between boys and girls were observed in the linear and angular velocity values associated with the lower extremity. The ground reaction force patterns also displayed differences for the boys and girls with the boys exhibiting a greater difference in the vertical peak force values, a greater braking force, and a greater value for the medio-lateral force excursion measure. The results provide a comprehensive description of the gait characteristics of children and suggest that differences between boys and girls are evident at age 3 and 4.
The quantitative assessment of children’s gait patterns has been an area of study for orthopaedic surgeons, podiatrists, physicians, physical therapists, and biomechanists. The purposes of these studies have included the development of normative data bases to be used in the diagnosis of pathological gait (Beck et al. 1981; and Sutherland et al. 1980) the design and evaluation of gait rehabilitation programs * Correspondence MN 55455. USA.
0167-9457/89/$3.50
address:
N.L. Greer,
University
of Minnesota,
0 1989, Elsevier Science Publishers
110 Cooke
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466
N. L. Greer et al. / Children’s gait
(Statham and Murray 1971), and the monitoring of progress in gait development as an indicator of neural and muscular development (Tylkowski 1986). It has been reported that one of the major weaknesses in the understanding of gait is the lack of a sufficiently broad data base for normal walking (Wall et al. 1986). The study of children’s gait has concentrated primarily on the measurement of temporal and spatial components (using a variety of footswitch and footprint tracing devices) and of kinematic parameters (using film or video techniques). Few attempts have been made to include ground reaction force measures in the analyses (Beck et al. 1981; and Noguchi et al. 1985). In addition, most of the studies have involved either a limited number of subjects or a limited number of trials per subject and, in most instances, only one day of testing was completed. The purpose of the present study, therefore, was to provide a comprehensive analysis of the dynamic characteristics of the gait of 3- and 4-year-old children as observed during multiple trials on two days. This age group was selected on the basis of previous research that has often resulted in the conclusion that a child has developed a full, mature gait cycle somewhere before 4 years of age (Tax 1977).
Methods
Subjects Eighteen children (7 boys and 11 girls) who were 3 and 4 years old at the time of the testing were volunteered by their parent/guardian to serve as subjects for the study. The children were reported by the parent/guardian to be free of any neuromuscular disorder or other condition that might influence the gait pattern. Prior to participation in the study, all procedures were explained to the parent/guardian and an informed consent document signed. Test schedule and protocol Following a session to familiarize the subject with the laboratory environment, 2 test sessions (scheduled one week apart and at approximately the same time of day each week) were completed. During each test session, the child performed 20 walking passes at his or her
N. L. Greer et al. / Chrldren’s gait
467
own pace along a walkway of approximately 6 meters in length. Each subject was barefoot and wearing either close fitting shorts and shirt or a leotard. Prior to the first test session, the child’s standing height and right leg length (from greater trochanter to lateral malleolus) were measured. The child’s mass was recorded on each of the test days. An AMTI force platform (Advanced Mechanical Technology, Inc., Newton, MA) was embedded in the raised walkway. The platform and the surrounding surface were covered with brown paper to conceal the exact location of the platform. In addition, ropes were placed on the floor to delineate a walking area that included only one half of the platform surface in an attempt to maximize the likelihood of the children striking the platform with only one foot. The subjects were unaware that they were to strike a particular area of the floor and they were instructed to walk the length of the rope-outlined walking area without touching the ropes and while focusing on a target placed above and at the end of the walkway. Infrared photoelectric sensors (Tandy Corporation, Fort Worth, TX) were placed before and after the force platform surface to provide a measure of the time taken to cover a 3.05 meter interval. Kinematic
analysis
Each of the walking trials was recorded on videotape using a NAC MOS Hi-Speed camera operating at 60 Hz. The optical axis of the camera was positioned perpendicular to the plane of walking to provide a sagittal view of the right side of the subject. Prior to each testing session, a reference measure was recorded on the videotape. This reference was later used to provide a conversion factor to actual units. Reflective tape markers (3M Corp., St. Paul, MN), approximately 1.3 cm square, were placed on the following anatomical landmarks: the base of the fifth metatarsal, the lateral malleolus, the junction of the tibia and femur, the greater trochanter of the femur, the acromion process, the elbow, and the wrist. The reflective markings, as recorded on the videotape, were converted to digital outlines and processed using the Motion Analysis Corp. (Santa Rosa, CA) video processor system and Expertvision software package. The resulting raw coordinate values were transferred to a microcomputer and smoothed using a recursive fourth-order zero phase shift digital filter. The optimal cut-off
468
N. L. Grew et al. / Children’s gait
frequency for each coordinate was determined according to the procedure described by Jackson (1979). The accuracy, precision, and overall performance of the video-based analysis system have been reported by Walton (1986). He observed that these characteristics of the system were comparable to what would be observed from manual digitization of 16 mm film. The smoothed coordinates were then used to calculate the temporal and kinematic variables. In addition to stride time and stride length, positional values for the segmental centers of gravity, the relative angles at the ankle, knee, hip, shoulder, and elbow and the absolute angles at the foot, shank, thigh, trunk, upper arm, and lower arm were determined. The locations of the segmental centers of gravity were determined according to the regression equations of Jensen (1986). Absolute angles were defined as the angle between a segment and a right directed horizontal line located at the distal end of the segment. The corresponding velocity measures were calculated using finite difference techniques. Five discrete points were identified in the gait cycle: heel strike, midstance (defined as the point when the hip and ankle markers were vertically aligned), toe-off, mid-swing (also defined by the alignment of the hip and ankle), and the second heel strike. By utilizing the displacement and velocity values at these five points, data from individual subjects could be compared. Ground reaction force analysis Output signals from the force platform were amplified (AMTI Amplifier Model SGA-3) and then sampled at a rate of 500 Hz using a Data Translation Model DT2801-A Analog and Digital I/O system board (Data Translation, Inc., Marlborough, MA). A total of 6 channels were monitored: forces along the 3 orthogonal axes and the associated moments about each axis. The data analysis focused on the 3 force components. In the vertical direction, three critical points were identified: the first maximum, the minimum, and the second maximum (fig. 1). At each of these points, the peak force value and the relative time (within the stance phase) to the occurrence of the peak force were recorded. An average vertical force and the support time were also determined.
N. L. Greer et al. / ChildrenS gait
Force
469
I
(N/kg)
a= b= c= d= e= f= g=
first maximum force, relative time to first maximum force, relative time to minimum force, minimum force, relative time to second maximum force, second maximum force, support time.
Fig. 1. Vertical ground
reaction
force variables.
In the antero-posterior direction, braking and propulsive phases were identified (fig. 2). Within each phase, the peak force and the relative time of the peak force were determined. In addition, the relative time of the transition from braking to propulsion was noted. From the medio-lateral data, the average force and the total force excursion were identified. The force excursion was defined as the sum of the absolute value of the changes in the medio-lateral force value in the transition from one point to the succeeding point:
Statistical procedures used in the data analysis included the calculation of means and standard deviations for each of the selected variables. In addition, product-moment correlation coefficients were assessed to examine the relationship between various gait variables and the age and anthropometric measures. Repeated measures analysis of variance procedures were used to determine the significance of differences between day 1 and day 2 results and between groups formed when the total sample was divided on the basis of sex. In all cases, the 0.05 level of significance was used.
470
N. L. Greer et al. / Chrldren’s gait
Force (N/kg) b
a= b= c= d= e=
relative time to maximum braking force. maximum braking force, relative time to zero force, relative time to maximum propulsion force, maximum propulsion force.
Fig. 2. Antero-posterior
ground
reaction
force variables.
Results Descriptive data for the subjects in the study are presented in table 1. When the children were grouped on the basis of sex, the only difference observed between the two groups was for the leg length value with the girls’ leg lengths significantly greater than those of the boys. Kinematic parameters For the kinematic analysis, 10 of the 20 trials completed on any one day were selected for further analysis. Selection of the trials was made
Table 1 Descriptive
statistics
(N = 18).
Variable Age (months) Age at independent walking Height(m) Right leg length (m) Mass (kg)
(months)
Mean
Standard
48.31 11.71 1.02 0.42 16.80
6.41 1.65 0.06 0.04 1.91
deviation
N. L. Grew et al. / Children’s gait
Table 2 Means and standard
deviations
for the temporal
and spatial
descriptors
Variable
Mean
Standard
Walking velocity (m/set) Stride length (m) Stride time (set) Right foot support time (set) Right foot swing time (set) Support/stride (48) Swing/stride (%)
1.21 0.84 0.74 0.33 0.42 43.86 56.14
0.21 0.12 0.08 0.07 0.04 5.53 5.53
411
(N = 17). deviation
on the basis of seveial criteria: the child was walking continuously throughout the field width, a full stride was visible in the video recording, and the reflective markers were properly located. The 10 trials selected were distributed throughout the 20 completed trials in order to better represent the total walking pattern on a given day. Due to a problem with the hip marker on one of the subjects, test data from only 17 of the 18 subjects (7 boys and 10 girls) were used in the kinematic analysis. Overall means and standard deviations for the temporal and spatial gait descriptors are presented in table 2. A repeated measures analysis of variance indicated that there were no significant differences between the day 1 and day 2 means for any of the variables studied. The boys had a longer swing phase time and a slightly longer overall stride time than the girls. The correlations between body measures and the temporal and spatial variables were low. Only the correlation between stride time and body mass (r = 0.52) exceeded r = 0.50. A correlation coefficient value of r = 0.48 was observed between height and stride length. Segmental linear resultant velocities were determined at each of the 5 points in the gait cycle (as previously defined). The values at the two heel strike points were similar and therefore only the first heel strike values are reported (table 3). The standard deviations of the velocity measures were relatively high resulting in coefficient of variation values in excess of 100% in some instances. For each segment, the linear velocity values on day 1 were not significantly different from those on day 2. Correlation coefficients describing the relationship of the segmental velocities and the anthropometric measures were computed. For the
472 Table 3 Resultant
N. L. Grew- et al. / Children’s gait
linear velocities
(m/set)
of the segmental
centers
of gravity
(N = 17)
Segment
Heel strike
Mid-stance
Toe-off
Mid-swing
Foot
0.60 a (0.22) 0.99 (0.23) 1.32 (0.25) 1.29 (0.22) 1.31 (0.27) 1.38 (0.87)
0.04 (0.05) 0.25 (0.13) 0.74 (0.20) 1.15 (0.22) 1.41 (0.29) 1.66
0.26 (0.13) 0.62 (0.24) 1.04 (0.22) 1.21 (0.21) 1.31 (0.30) 1.42 (0.44)
3.55 (0.55) 2.29 (0.40) 1.38 (0.29) 1.21 (0.23) 1.01 (0.22) 0.80 (0.29)
Shank Thigh Trunk Upper arm Lower arm
a Mean (Standard
(0.44)
deviation)
foot segment, correlations above r = 0.50 (all significant) were observed for the association of height and resultant velocity at mid-swing (r = 0.57) and body mass and resultant velocity at mid-swing (r = - 0.56). None of the other correlations involving the resultant velocity exceeded r = 0.50. When the subjects were divided into groups on the basis of sex, several significant differences were noted. For the boys, the vertical velocities of both the foot and shank segments at the heel strike point were greater than for the girls. At both heel strike and mid-swing, the boys had a greater vertical velocity of the thigh while the girls displayed a greater horizontal and resultant velocity of the thigh at toe-off. The trunk and upper arm segments of the boys also showed greater vertical velocity values at heel strike and at mid-swing while no differences were observed for the lower arm segment. Relative angle measures and the associated velocities are presented in table 4. Large standard deviations were noted especially for the velocity values. Overall, the variability associated with the measures at the shoulder and elbow appeared to be greater than for the other angles evaluated in this study. A comparison of results on day 1 and day 2 indicated differences only for the ankle angle with greater values on the second day at each of the 5 points identified in the gait cycle. Correlations between the relative angle variables and the age and anthropometric measures were generally low. Correlations that ex-
N. L. Greer et al. / Children’s gait
473
Table 4 Relative
angles (deg) and angular velocities
Variable
Heel strike
(deg/sec)
Mid-stance
(N = 17). Toe-off
Mid-swing
Ankle Angle
116.96 a (10.10)
Angular
vel.
105.07 (9.58)
103.51 (8.73)
105.60 (9.97)
- 108.77
- 61.52
38.81
- 35.40
(107.88)
(69.21)
(5.84)
(161.12)
170.57
160.36
Knee Angle Angular
vel.
169.82
128.77 (10.56)
(10.17)
(8.58)
71.51
- 83.61
492.47
(7.6?)
(106.05)
(129.38)
(108.17)
160.92
170.64
165.54
156.69
(7.46) - 129.30
Hip Angle
(9.67) Angular
vel.
(6.98)
37.54
105.26
(63.91)
(115.60)
(8.21) -65.52 (80.18)
(7.87) - 43.97 (52.52)
Shoulder Angle Angular
vel.
- 27.16
18.15
13.44
17.41
(13.19)
(11.55)
(10.90)
(11.22)
19.04
- 116.63
28.13
100.41
(66.12)
(111.60)
(106.29)
(105.98)
148.46
150.37
141.04
145.98
(25.63)
(22.32)
(20.42)
(21.76)
46.58
- 29.35
- 37.98
9.70
(102.04)
(140.66)
(126.12)
(131.22)
Elbow Angle Angular
vel.
a Mean (Standard
deviation).
ceeded r = 0.50 were noted between age and mid-swing angular velocity of the knee (r = -0.69) and hip (r = - 0.59), age and mid-stance velocity of the elbow (r = - 0.50), age of walking and angle of the ankle at heel strike (r = -0.52), age of walking and the mid-stance velocity of the shoulder (r = 0.58), and age of walking and the mid-swing velocity of the elbow (r = - 0.57). A comparison between boys and girls resulted in the identification of significant differences in the measures for the knee angle at mid-stance and the knee angular velocity at toe-off. The absolute angle and angular velocity values are presented in table 5. The standard deviations associated with measurements from the more distal segments (foot, upper arm, lower arm) appear to be greater than those associated with the more proximal segments (shank, thigh,
N. L. Greer et al. / Children’s gait
474 Table
5
Absolute
angles (deg) and angular velocities
Variable
Heel strike
(deg/sec)
Mid-stance
(N = 17). Toe-off
Mid-swing
Foot Angle Angular
vel.
168.43 a
155.91
- 138.04
(18.77)
(14.01)
(12.91)
138.12 (16.96)
- 46.39
- 255.03
574.72
(96.57)
(86.79)
(120.97)
(198.26)
105.44
82.24
62.64
65.01
(4.76)
(7.57)
-73.73
Shank Angle
(5.89) Angular
vel.
(6.76)
~ 182.34
- 113.29
- 189.89
550.85
(77.35)
(58.63)
(61.61)
(110.80)
113.41
101.44
71.96
115.22
Thigh Angle
(7.70) Angular
vel.
(6.37)
(8.37)
(6.71)
- 20.56
- 184.58
- 90.30
62.79
(55.19)
(71.59)
(87.26)
(49.32)
95.05
93.70
85.22
92.41
(5.13)
(5.54)
(5.14)
Trunk Angle Angular
vel.
(4.78)
17.94
- 43.50
~ 12.06
21.60
(27.89)
(30.84)
(30.22)
(20.78)
Upper arm Angle Angular
vel.
70.14
78.39
92.90
77.75
(16.18)
(13.76)
(14.63)
(14.60)
33.94
93.85
42.19
- 101.76
(61.77)
(88.18)
(85.58)
(82.07)
100.99
107.86
130.23
110.44
(30.52)
(25.98)
(23.67)
(25.59)
- 14.56
126.04
69.91
- 109.84
(101.42)
(160.26)
(159.31)
(143.47)
Lower arm Angle Angular
vel.
a Mean (Standard
deviation).
trunk). Differences between day 1 and day 2 values were observed for the foot angle at all 5 points in the gait cycle and for the trunk angle at take-off. In each case, the value for the angle was smaller on the second day. Again, the correlation values were generally low. Correlations above Y= 0.50 were observed between age and the shank velocity at mid-stance the angle of (r = 0.50) the s h an k velocity at mid-swing (r = -0.65) the lower arm at heel strike (r = - 0.50), and the lower arm velocity at mid-stance (Y = 0.53). Leg length was correlated above r = 0.50 with
N. L. Greer et al. / Children’s gait
475
the angle of the trunk at toe-off (Y = 0.62), the angle of the trunk at mid-swing (r = 0.50), the velocity of the trunk at mid-swing (r = - 0.60) and the angle of the thigh at mid-stance (Y = -0.58). Body mass was correlated with mid-swing velocity of the thigh (r = 0.53). Significant differences between the boys and girls were observed for the angular velocity of the shank and thigh segments at heel strike and the angle of the shank and thigh segments at mid-stance. For the shank, the boys displayed a larger negative velocity at heel strike and a smaller angle at mid-stance than the girls, while for the thigh, the pattern was reversed with the girls exhibiting a larger negative velocity at heel strike and a smaller angle at mid-stance. The trunk angle at toe-off was greater for the girls than for the boys. No significant differences were noted for the upper or lower arm segments. Ground reaction force parameters It was not possible to control the consistency with which the children struck the force platform. As a result, each child had a different number of successful trials on a given test day. A preliminary analysis, using data from 5 subjects randomly selected from among those who had a minimum of 6 successful trials on each test day, examined the pattern of test results across trials. No trend was apparent in the responses and it was decided, therefore, to use all of the acceptable trials for a given subject on a given day to represent that subject’s performance. Tables 6 and 7 display the means and standard deviations for the ground reaction force variables. The coefficient of variation values was generally about 10% although for several variables, the value was considerably higher. A comparison of day 1 and day 2 means resulted in two significant differences: the relative time to the second vertical maximum force and the average antero-posterior braking force. The relative time was greater and the braking force higher on day 2 than on day 1. Several significant differences were noted between the boys and girls. In the vertical direction, the boys had a greater value for the relative time to the minimum force and a lower minimum force value. An additional variable, the ratio between the first and second maximum vertical forces, was also significantly greater for the boys than the girls (1.51 and 1.22, respectively).
N. L. Greer ef al. / Children’s gait
476 Table 6 Means and standard
deviations
for selected vertical
ground
reaction
force components
Variable
Mean
Standard
Relative time to 1st max. force a First max. force b Relative time to minimum force Minimum force Relative time to 2nd max. force Second max. force Average force Support time (set)
22.17 12.42 48.87 5.66 76.23 9.43 1.73 0.43
1.69 1.69 4.06 1.00 2.51 0.95 0.50 0.04
(N = 18).
deviation
a Percent of stance time. ’ All forces in N/kg.
In the antero-posterior direction, a significant difference was observed for the maximum braking force with a greater force value for the boys. The medio-lateral force excursion value was also significantly greater for the boys. Only leg length correlated above r = 0.50 with any of the ground reaction force measures. A correlation of Y= - 0.58 was observed between leg length and the maximum propulsion force (antero-posterior direction) and a correlation of r = - 0.53 was observed for the relationship between leg length and the force excursion measure.
Table 7 Mrsr,~ and standard deviations force components (N = 18).
for selected
antero-posterior
and medio-lateral
Mean
Standard
14.14 - 1.81 31.69 84.43 1.82
1.86 0.52 4.22 0.68 0.31
0.28 5.43
0.10 1.02
ground
-._. Varicliie Antero-posterior Relative time to max. brake force a Max. brake force b Relative time to zero force Relative time to max. propulsion Max. propulsion
force
force
Mediclateral Average force Force excursions a Percent of stance time. ’ All forces in N/kg.
deviation
reaction
N. L. Greer et al. / Children’s gart
477
Discussion Temporal and spatial characteristics of children’s gait have frequently been measured as many of the variables may be evaluated without the use of expensive, technical equipment. The results of the present study are in agreement with many of the previously reported findings. The overall mean walking velocity of 1.21 m/set was similar to the fast walking speed trials of Beck et al. (1981) and Slaton (1985) who reported values of 1.25 and 1.29 m/set, respectively, for subjects in this age range. The observed stride length of 0.84 meters was also in agreement with the previously reported values (Beck et al. 1981; and Rose-Jacobs 1983) although, unlike the findings of Norlin et al. (1981) the stride lengths for the girls did not exceed those for the boys. The mean stride time (0.74 set) was identical to the value reported by Slaton who had also observed no significant correlations between the stride time measures and the anthropometric measures or age variables, a finding substantiated by the present study. Many of the commonly used descriptors of gait have been found to be correlated with walking velocity. Although the walking velocity on day 1 (1.20 m/set) was not significantly different than on day 2 (1.19 m/set), for a given subject, the coefficient of variation values for the variability over trials ranged from 3 to 31%. This would indicate that for some subjects the velocity values did differ considerably from trial to trial. With the age range selected for study, it was not possible to control the walking velocity or to analyze only those trials that fell within a certain tolerance of a desired walking velocity. It was also decided that normalizing by walking velocity tended to produce artificial, less meaningful, measures. Differences between boys and girls were observed for the segmental center of gravity velocity values, notably the vertical velocity of the lower extremity segments at heel strike and the vertical velocity of the thigh and trunk at both heel strike and mid-swing. Subjectively, the boys tended to walk with a more ‘bouncy’ gait showing greater vertical displacement of the anatomical markers throughout the gait cycle. The significant differences in the vertical velocity measures may lend quantitative support to the visual observation of sex differences in the walking style. Comparison of the values obtained in the present study with previ-
478
N.L. Greer et al. / Children’s g-art
ous research is difficult as many of the studies did not report complete results. It is interesting to note that although their data was derived from children 6 years of age and older, Foley et al. (1979) reported similar standard deviation values and a similar pattern of lower values for the more proximal segments. The results of the relative and absolute angle and angular velocity calculations present many similarities. Significant differences between days were observed for the foot and ankle angles while few differences were noted between boys and girls for any of the angle measurements. Several significant correlations were observed between age and the relative angular velocity measures at the mid-swing point of the gait cycle. The negative correlation coefficients would indicate that the older children tended to have lower angular velocity values than did the younger children. A decrease in the angular velocity values associated with a segment may reflect the establishment of a smoother gait pattern. From the ground reaction force data, it is interesting to note the differences between the boys and girls and the relationship between the force values and the results of the kinematic analysis. The minimum vertical force occurs at approximately the point where the center of gravity of the body passes over the base of support. A lower minimum force value corresponds with greater knee flexion resulting in a lower center of gravity position. The results indicated that the boys had both a lower minimum force value and greater flexion of the knee at the mid-stance point. The relative time to the minimum force was longer for the boys than the girls. This would be expected as the knee angle was not different at the point of contact with the force platform but then became significantly less (more flexed) at the mid-stance point. There were no significant differences in the knee angular velocities at either the heel strike or mid-stance points. Based on a visual examination of the vertical ground reaction force curves, a ratio between the first and second maximum force values was determined. The ratio values were significantly different for the boys and girls (with a greater value for the boys). It is possible that this ratio may be reflective of the developmental stage of the gait pattern. Noguchi et al. (1985) reported higher vertical heel strike forces than push off forces although no distinction was made between boys and girls.
N. L. Grew et al. / Chddren’s gait
479
The point of transition from braking to propulsion (in an anteroposterior direction) occurred earlier in children than in adults. The expected transition point would be at approximately 50% of the stance phase while in the present study, the transition occurred at 37.7%. Noguchi et al. (1985) also reported an earlier transition point for children. The boys displayed a higher value for the medio-lateral force excursions variable. This variable reflects greater changes in the medio-lateral force between successive data samples. A higher value may indicate greater movement of the foot or of the total body over the foot and may also be reflective of a less developed gait pattern. Noguchi et al. (1985) had noted that the medio-lateral force pattern was the last of the three force components to mature. The results of the present study provide a description of the temporal and spatial, kinematic, and ground reaction force characteristics of the gait of 3- and 4-year-old children. The identification of differences between boys and girls represented a secondary question. When considering the results, it should be remembered that the large number of analyses completed may have contributed to a chance finding of significance. In addition, when the children were divided into sub-groups, the resulting sample sizes may have been insufficient to identify true differences between the groups. Nevertheless, it would appear that even at age 3 and 4, differences between boys and girls should be considered.
References Beck, R.J., T.P. Andriacchi, K.N. Kuo, Fermier and J.O. Galante, 1981. Changes in the gait patterns of growing children. Journal of Bone and Joint Surgery 63A, 1452-1457. Foley, C.D., A.O. Quanbury and T. Steinke, 1979. Kinematics of normal child locomotion-a statistical study based on TV data. Journal of Biomechanics 12, 1-8. Jackson, K.M., 1979. Fitting of mathematical functions to biomechanical data. IEEE Transactions on Biomedical Engineering 26, 122-124. Jensen, R.K., 1986. Body segment mass, radius, and radius of gyration proportions of children. Journal of Biomechanics 19, 359-368. Noguchi, M., A. Hamamura, N. Matsusaka, M. Fujita, T. Norimatsu and S. Ikeda, 1985. ‘Development of gait in childhood’. In: D.A. Winter, R.W. Norman, R.P. Wells, K.C. Hayes and A.E. Patla (eds.), Biomechanics IX-A Champaign, IL: Human Kinetics Publishers. Norlin, R., P. Odenrick and B. Sandlund, 1981. Development of gait in the normal child. Journal of Pediatric Orthopedics 1, 261-266.
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Greer el al. / Children’s
gazt
Rose-Jacobs, R., 1983. Development of gait at slow, free, and fast speeds in 3- and 5-year-old children. Physical Therapy 63, 1251-1259. Slaton, D.S., 1985. Gait cycle duration in 3-year-old children. Physical Therapy 65, 17-21. Statham, L. and M.P. Murray, 1971. Early walking patterns of normal children. Clinical Orthopaedics and Related Research 79, 8824. Sutherland, D.H., R. Olshen. L. Cooper and S.L.-Y. Woo, 1980. The development of mature gait. Journal of Bone and Joint Surgery 62A, 336-353. Tax. H.R., 1977. Locomotion and the child patient. Journal of the American Podiatry Association 67, 96-101. Tylkowski, C.M., 1986. ‘Assessment of gait in children and adolescents’. In: W.W. Love11 and R.B. Winter (eds.), Pediatric orthopaedics. Philadelphia, PA: J.B. Lippincott. Co. pp. 1061~1081. Wall, J.C., J. Charteris and C.I. Turnbull, 1986. The diversity of normal gait. Proceedings of the North American Congress in Biomechanics, Montreal, Canada. pp. 224-225. Walton, J.S., 1986. The accuracy and precision of a video-based motion analysis system. Proceedings of the 30th International Technical Symposium on Optical and Optoelectronic Applied Sciences and Engineering, 693, San Diego, CA. pp. 17-22.
Science 8 (1989) 465-480
DYNAMICS
OF CHILDREN’S
Nancy
L. GREER
University of Minnesota,
GAIT
* Mwmeapolis,
Joseph
HAMILL
University
of Massachusetts,
Amherst,
USA
USA
Kevin R. CAMPBELL Cleveland Clinic Foundation,
USA
Greer, N.L., J. Hamill and K.R. Campbell, 1989. Dynamics gait. Human Movement Science 8, 465-480.
of children’s
The purpose of the present study was to examine the characteristics of gait in 3- and 4-year-old children. Eighteen children completed 20 walking passes on each of two days. Sagittal plane kinematics and ground reaction force patterns were analyzed. From the kinematic data, high standard deviation values were noted for many of the segmental and angular velocity variables, especially the more distal segments and joints. Differences between boys and girls were observed in the linear and angular velocity values associated with the lower extremity. The ground reaction force patterns also displayed differences for the boys and girls with the boys exhibiting a greater difference in the vertical peak force values, a greater braking force, and a greater value for the medio-lateral force excursion measure. The results provide a comprehensive description of the gait characteristics of children and suggest that differences between boys and girls are evident at age 3 and 4.
The quantitative assessment of children’s gait patterns has been an area of study for orthopaedic surgeons, podiatrists, physicians, physical therapists, and biomechanists. The purposes of these studies have included the development of normative data bases to be used in the diagnosis of pathological gait (Beck et al. 1981; and Sutherland et al. 1980) the design and evaluation of gait rehabilitation programs * Correspondence MN 55455. USA.
0167-9457/89/$3.50
address:
N.L. Greer,
University
of Minnesota,
0 1989, Elsevier Science Publishers
110 Cooke
B.V. (North-Holland)
Hall, Minneapolis,
466
N. L. Greer et al. / Children’s gait
(Statham and Murray 1971), and the monitoring of progress in gait development as an indicator of neural and muscular development (Tylkowski 1986). It has been reported that one of the major weaknesses in the understanding of gait is the lack of a sufficiently broad data base for normal walking (Wall et al. 1986). The study of children’s gait has concentrated primarily on the measurement of temporal and spatial components (using a variety of footswitch and footprint tracing devices) and of kinematic parameters (using film or video techniques). Few attempts have been made to include ground reaction force measures in the analyses (Beck et al. 1981; and Noguchi et al. 1985). In addition, most of the studies have involved either a limited number of subjects or a limited number of trials per subject and, in most instances, only one day of testing was completed. The purpose of the present study, therefore, was to provide a comprehensive analysis of the dynamic characteristics of the gait of 3- and 4-year-old children as observed during multiple trials on two days. This age group was selected on the basis of previous research that has often resulted in the conclusion that a child has developed a full, mature gait cycle somewhere before 4 years of age (Tax 1977).
Methods
Subjects Eighteen children (7 boys and 11 girls) who were 3 and 4 years old at the time of the testing were volunteered by their parent/guardian to serve as subjects for the study. The children were reported by the parent/guardian to be free of any neuromuscular disorder or other condition that might influence the gait pattern. Prior to participation in the study, all procedures were explained to the parent/guardian and an informed consent document signed. Test schedule and protocol Following a session to familiarize the subject with the laboratory environment, 2 test sessions (scheduled one week apart and at approximately the same time of day each week) were completed. During each test session, the child performed 20 walking passes at his or her
N. L. Greer et al. / Chrldren’s gait
467
own pace along a walkway of approximately 6 meters in length. Each subject was barefoot and wearing either close fitting shorts and shirt or a leotard. Prior to the first test session, the child’s standing height and right leg length (from greater trochanter to lateral malleolus) were measured. The child’s mass was recorded on each of the test days. An AMTI force platform (Advanced Mechanical Technology, Inc., Newton, MA) was embedded in the raised walkway. The platform and the surrounding surface were covered with brown paper to conceal the exact location of the platform. In addition, ropes were placed on the floor to delineate a walking area that included only one half of the platform surface in an attempt to maximize the likelihood of the children striking the platform with only one foot. The subjects were unaware that they were to strike a particular area of the floor and they were instructed to walk the length of the rope-outlined walking area without touching the ropes and while focusing on a target placed above and at the end of the walkway. Infrared photoelectric sensors (Tandy Corporation, Fort Worth, TX) were placed before and after the force platform surface to provide a measure of the time taken to cover a 3.05 meter interval. Kinematic
analysis
Each of the walking trials was recorded on videotape using a NAC MOS Hi-Speed camera operating at 60 Hz. The optical axis of the camera was positioned perpendicular to the plane of walking to provide a sagittal view of the right side of the subject. Prior to each testing session, a reference measure was recorded on the videotape. This reference was later used to provide a conversion factor to actual units. Reflective tape markers (3M Corp., St. Paul, MN), approximately 1.3 cm square, were placed on the following anatomical landmarks: the base of the fifth metatarsal, the lateral malleolus, the junction of the tibia and femur, the greater trochanter of the femur, the acromion process, the elbow, and the wrist. The reflective markings, as recorded on the videotape, were converted to digital outlines and processed using the Motion Analysis Corp. (Santa Rosa, CA) video processor system and Expertvision software package. The resulting raw coordinate values were transferred to a microcomputer and smoothed using a recursive fourth-order zero phase shift digital filter. The optimal cut-off
468
N. L. Grew et al. / Children’s gait
frequency for each coordinate was determined according to the procedure described by Jackson (1979). The accuracy, precision, and overall performance of the video-based analysis system have been reported by Walton (1986). He observed that these characteristics of the system were comparable to what would be observed from manual digitization of 16 mm film. The smoothed coordinates were then used to calculate the temporal and kinematic variables. In addition to stride time and stride length, positional values for the segmental centers of gravity, the relative angles at the ankle, knee, hip, shoulder, and elbow and the absolute angles at the foot, shank, thigh, trunk, upper arm, and lower arm were determined. The locations of the segmental centers of gravity were determined according to the regression equations of Jensen (1986). Absolute angles were defined as the angle between a segment and a right directed horizontal line located at the distal end of the segment. The corresponding velocity measures were calculated using finite difference techniques. Five discrete points were identified in the gait cycle: heel strike, midstance (defined as the point when the hip and ankle markers were vertically aligned), toe-off, mid-swing (also defined by the alignment of the hip and ankle), and the second heel strike. By utilizing the displacement and velocity values at these five points, data from individual subjects could be compared. Ground reaction force analysis Output signals from the force platform were amplified (AMTI Amplifier Model SGA-3) and then sampled at a rate of 500 Hz using a Data Translation Model DT2801-A Analog and Digital I/O system board (Data Translation, Inc., Marlborough, MA). A total of 6 channels were monitored: forces along the 3 orthogonal axes and the associated moments about each axis. The data analysis focused on the 3 force components. In the vertical direction, three critical points were identified: the first maximum, the minimum, and the second maximum (fig. 1). At each of these points, the peak force value and the relative time (within the stance phase) to the occurrence of the peak force were recorded. An average vertical force and the support time were also determined.
N. L. Greer et al. / ChildrenS gait
Force
469
I
(N/kg)
a= b= c= d= e= f= g=
first maximum force, relative time to first maximum force, relative time to minimum force, minimum force, relative time to second maximum force, second maximum force, support time.
Fig. 1. Vertical ground
reaction
force variables.
In the antero-posterior direction, braking and propulsive phases were identified (fig. 2). Within each phase, the peak force and the relative time of the peak force were determined. In addition, the relative time of the transition from braking to propulsion was noted. From the medio-lateral data, the average force and the total force excursion were identified. The force excursion was defined as the sum of the absolute value of the changes in the medio-lateral force value in the transition from one point to the succeeding point:
Statistical procedures used in the data analysis included the calculation of means and standard deviations for each of the selected variables. In addition, product-moment correlation coefficients were assessed to examine the relationship between various gait variables and the age and anthropometric measures. Repeated measures analysis of variance procedures were used to determine the significance of differences between day 1 and day 2 results and between groups formed when the total sample was divided on the basis of sex. In all cases, the 0.05 level of significance was used.
470
N. L. Greer et al. / Chrldren’s gait
Force (N/kg) b
a= b= c= d= e=
relative time to maximum braking force. maximum braking force, relative time to zero force, relative time to maximum propulsion force, maximum propulsion force.
Fig. 2. Antero-posterior
ground
reaction
force variables.
Results Descriptive data for the subjects in the study are presented in table 1. When the children were grouped on the basis of sex, the only difference observed between the two groups was for the leg length value with the girls’ leg lengths significantly greater than those of the boys. Kinematic parameters For the kinematic analysis, 10 of the 20 trials completed on any one day were selected for further analysis. Selection of the trials was made
Table 1 Descriptive
statistics
(N = 18).
Variable Age (months) Age at independent walking Height(m) Right leg length (m) Mass (kg)
(months)
Mean
Standard
48.31 11.71 1.02 0.42 16.80
6.41 1.65 0.06 0.04 1.91
deviation
N. L. Grew et al. / Children’s gait
Table 2 Means and standard
deviations
for the temporal
and spatial
descriptors
Variable
Mean
Standard
Walking velocity (m/set) Stride length (m) Stride time (set) Right foot support time (set) Right foot swing time (set) Support/stride (48) Swing/stride (%)
1.21 0.84 0.74 0.33 0.42 43.86 56.14
0.21 0.12 0.08 0.07 0.04 5.53 5.53
411
(N = 17). deviation
on the basis of seveial criteria: the child was walking continuously throughout the field width, a full stride was visible in the video recording, and the reflective markers were properly located. The 10 trials selected were distributed throughout the 20 completed trials in order to better represent the total walking pattern on a given day. Due to a problem with the hip marker on one of the subjects, test data from only 17 of the 18 subjects (7 boys and 10 girls) were used in the kinematic analysis. Overall means and standard deviations for the temporal and spatial gait descriptors are presented in table 2. A repeated measures analysis of variance indicated that there were no significant differences between the day 1 and day 2 means for any of the variables studied. The boys had a longer swing phase time and a slightly longer overall stride time than the girls. The correlations between body measures and the temporal and spatial variables were low. Only the correlation between stride time and body mass (r = 0.52) exceeded r = 0.50. A correlation coefficient value of r = 0.48 was observed between height and stride length. Segmental linear resultant velocities were determined at each of the 5 points in the gait cycle (as previously defined). The values at the two heel strike points were similar and therefore only the first heel strike values are reported (table 3). The standard deviations of the velocity measures were relatively high resulting in coefficient of variation values in excess of 100% in some instances. For each segment, the linear velocity values on day 1 were not significantly different from those on day 2. Correlation coefficients describing the relationship of the segmental velocities and the anthropometric measures were computed. For the
472 Table 3 Resultant
N. L. Grew- et al. / Children’s gait
linear velocities
(m/set)
of the segmental
centers
of gravity
(N = 17)
Segment
Heel strike
Mid-stance
Toe-off
Mid-swing
Foot
0.60 a (0.22) 0.99 (0.23) 1.32 (0.25) 1.29 (0.22) 1.31 (0.27) 1.38 (0.87)
0.04 (0.05) 0.25 (0.13) 0.74 (0.20) 1.15 (0.22) 1.41 (0.29) 1.66
0.26 (0.13) 0.62 (0.24) 1.04 (0.22) 1.21 (0.21) 1.31 (0.30) 1.42 (0.44)
3.55 (0.55) 2.29 (0.40) 1.38 (0.29) 1.21 (0.23) 1.01 (0.22) 0.80 (0.29)
Shank Thigh Trunk Upper arm Lower arm
a Mean (Standard
(0.44)
deviation)
foot segment, correlations above r = 0.50 (all significant) were observed for the association of height and resultant velocity at mid-swing (r = 0.57) and body mass and resultant velocity at mid-swing (r = - 0.56). None of the other correlations involving the resultant velocity exceeded r = 0.50. When the subjects were divided into groups on the basis of sex, several significant differences were noted. For the boys, the vertical velocities of both the foot and shank segments at the heel strike point were greater than for the girls. At both heel strike and mid-swing, the boys had a greater vertical velocity of the thigh while the girls displayed a greater horizontal and resultant velocity of the thigh at toe-off. The trunk and upper arm segments of the boys also showed greater vertical velocity values at heel strike and at mid-swing while no differences were observed for the lower arm segment. Relative angle measures and the associated velocities are presented in table 4. Large standard deviations were noted especially for the velocity values. Overall, the variability associated with the measures at the shoulder and elbow appeared to be greater than for the other angles evaluated in this study. A comparison of results on day 1 and day 2 indicated differences only for the ankle angle with greater values on the second day at each of the 5 points identified in the gait cycle. Correlations between the relative angle variables and the age and anthropometric measures were generally low. Correlations that ex-
N. L. Greer et al. / Children’s gait
473
Table 4 Relative
angles (deg) and angular velocities
Variable
Heel strike
(deg/sec)
Mid-stance
(N = 17). Toe-off
Mid-swing
Ankle Angle
116.96 a (10.10)
Angular
vel.
105.07 (9.58)
103.51 (8.73)
105.60 (9.97)
- 108.77
- 61.52
38.81
- 35.40
(107.88)
(69.21)
(5.84)
(161.12)
170.57
160.36
Knee Angle Angular
vel.
169.82
128.77 (10.56)
(10.17)
(8.58)
71.51
- 83.61
492.47
(7.6?)
(106.05)
(129.38)
(108.17)
160.92
170.64
165.54
156.69
(7.46) - 129.30
Hip Angle
(9.67) Angular
vel.
(6.98)
37.54
105.26
(63.91)
(115.60)
(8.21) -65.52 (80.18)
(7.87) - 43.97 (52.52)
Shoulder Angle Angular
vel.
- 27.16
18.15
13.44
17.41
(13.19)
(11.55)
(10.90)
(11.22)
19.04
- 116.63
28.13
100.41
(66.12)
(111.60)
(106.29)
(105.98)
148.46
150.37
141.04
145.98
(25.63)
(22.32)
(20.42)
(21.76)
46.58
- 29.35
- 37.98
9.70
(102.04)
(140.66)
(126.12)
(131.22)
Elbow Angle Angular
vel.
a Mean (Standard
deviation).
ceeded r = 0.50 were noted between age and mid-swing angular velocity of the knee (r = -0.69) and hip (r = - 0.59), age and mid-stance velocity of the elbow (r = - 0.50), age of walking and angle of the ankle at heel strike (r = -0.52), age of walking and the mid-stance velocity of the shoulder (r = 0.58), and age of walking and the mid-swing velocity of the elbow (r = - 0.57). A comparison between boys and girls resulted in the identification of significant differences in the measures for the knee angle at mid-stance and the knee angular velocity at toe-off. The absolute angle and angular velocity values are presented in table 5. The standard deviations associated with measurements from the more distal segments (foot, upper arm, lower arm) appear to be greater than those associated with the more proximal segments (shank, thigh,
N. L. Greer et al. / Children’s gait
474 Table
5
Absolute
angles (deg) and angular velocities
Variable
Heel strike
(deg/sec)
Mid-stance
(N = 17). Toe-off
Mid-swing
Foot Angle Angular
vel.
168.43 a
155.91
- 138.04
(18.77)
(14.01)
(12.91)
138.12 (16.96)
- 46.39
- 255.03
574.72
(96.57)
(86.79)
(120.97)
(198.26)
105.44
82.24
62.64
65.01
(4.76)
(7.57)
-73.73
Shank Angle
(5.89) Angular
vel.
(6.76)
~ 182.34
- 113.29
- 189.89
550.85
(77.35)
(58.63)
(61.61)
(110.80)
113.41
101.44
71.96
115.22
Thigh Angle
(7.70) Angular
vel.
(6.37)
(8.37)
(6.71)
- 20.56
- 184.58
- 90.30
62.79
(55.19)
(71.59)
(87.26)
(49.32)
95.05
93.70
85.22
92.41
(5.13)
(5.54)
(5.14)
Trunk Angle Angular
vel.
(4.78)
17.94
- 43.50
~ 12.06
21.60
(27.89)
(30.84)
(30.22)
(20.78)
Upper arm Angle Angular
vel.
70.14
78.39
92.90
77.75
(16.18)
(13.76)
(14.63)
(14.60)
33.94
93.85
42.19
- 101.76
(61.77)
(88.18)
(85.58)
(82.07)
100.99
107.86
130.23
110.44
(30.52)
(25.98)
(23.67)
(25.59)
- 14.56
126.04
69.91
- 109.84
(101.42)
(160.26)
(159.31)
(143.47)
Lower arm Angle Angular
vel.
a Mean (Standard
deviation).
trunk). Differences between day 1 and day 2 values were observed for the foot angle at all 5 points in the gait cycle and for the trunk angle at take-off. In each case, the value for the angle was smaller on the second day. Again, the correlation values were generally low. Correlations above Y= 0.50 were observed between age and the shank velocity at mid-stance the angle of (r = 0.50) the s h an k velocity at mid-swing (r = -0.65) the lower arm at heel strike (r = - 0.50), and the lower arm velocity at mid-stance (Y = 0.53). Leg length was correlated above r = 0.50 with
N. L. Greer et al. / Children’s gait
475
the angle of the trunk at toe-off (Y = 0.62), the angle of the trunk at mid-swing (r = 0.50), the velocity of the trunk at mid-swing (r = - 0.60) and the angle of the thigh at mid-stance (Y = -0.58). Body mass was correlated with mid-swing velocity of the thigh (r = 0.53). Significant differences between the boys and girls were observed for the angular velocity of the shank and thigh segments at heel strike and the angle of the shank and thigh segments at mid-stance. For the shank, the boys displayed a larger negative velocity at heel strike and a smaller angle at mid-stance than the girls, while for the thigh, the pattern was reversed with the girls exhibiting a larger negative velocity at heel strike and a smaller angle at mid-stance. The trunk angle at toe-off was greater for the girls than for the boys. No significant differences were noted for the upper or lower arm segments. Ground reaction force parameters It was not possible to control the consistency with which the children struck the force platform. As a result, each child had a different number of successful trials on a given test day. A preliminary analysis, using data from 5 subjects randomly selected from among those who had a minimum of 6 successful trials on each test day, examined the pattern of test results across trials. No trend was apparent in the responses and it was decided, therefore, to use all of the acceptable trials for a given subject on a given day to represent that subject’s performance. Tables 6 and 7 display the means and standard deviations for the ground reaction force variables. The coefficient of variation values was generally about 10% although for several variables, the value was considerably higher. A comparison of day 1 and day 2 means resulted in two significant differences: the relative time to the second vertical maximum force and the average antero-posterior braking force. The relative time was greater and the braking force higher on day 2 than on day 1. Several significant differences were noted between the boys and girls. In the vertical direction, the boys had a greater value for the relative time to the minimum force and a lower minimum force value. An additional variable, the ratio between the first and second maximum vertical forces, was also significantly greater for the boys than the girls (1.51 and 1.22, respectively).
N. L. Greer ef al. / Children’s gait
476 Table 6 Means and standard
deviations
for selected vertical
ground
reaction
force components
Variable
Mean
Standard
Relative time to 1st max. force a First max. force b Relative time to minimum force Minimum force Relative time to 2nd max. force Second max. force Average force Support time (set)
22.17 12.42 48.87 5.66 76.23 9.43 1.73 0.43
1.69 1.69 4.06 1.00 2.51 0.95 0.50 0.04
(N = 18).
deviation
a Percent of stance time. ’ All forces in N/kg.
In the antero-posterior direction, a significant difference was observed for the maximum braking force with a greater force value for the boys. The medio-lateral force excursion value was also significantly greater for the boys. Only leg length correlated above r = 0.50 with any of the ground reaction force measures. A correlation of Y= - 0.58 was observed between leg length and the maximum propulsion force (antero-posterior direction) and a correlation of r = - 0.53 was observed for the relationship between leg length and the force excursion measure.
Table 7 Mrsr,~ and standard deviations force components (N = 18).
for selected
antero-posterior
and medio-lateral
Mean
Standard
14.14 - 1.81 31.69 84.43 1.82
1.86 0.52 4.22 0.68 0.31
0.28 5.43
0.10 1.02
ground
-._. Varicliie Antero-posterior Relative time to max. brake force a Max. brake force b Relative time to zero force Relative time to max. propulsion Max. propulsion
force
force
Mediclateral Average force Force excursions a Percent of stance time. ’ All forces in N/kg.
deviation
reaction
N. L. Greer et al. / Children’s gart
477
Discussion Temporal and spatial characteristics of children’s gait have frequently been measured as many of the variables may be evaluated without the use of expensive, technical equipment. The results of the present study are in agreement with many of the previously reported findings. The overall mean walking velocity of 1.21 m/set was similar to the fast walking speed trials of Beck et al. (1981) and Slaton (1985) who reported values of 1.25 and 1.29 m/set, respectively, for subjects in this age range. The observed stride length of 0.84 meters was also in agreement with the previously reported values (Beck et al. 1981; and Rose-Jacobs 1983) although, unlike the findings of Norlin et al. (1981) the stride lengths for the girls did not exceed those for the boys. The mean stride time (0.74 set) was identical to the value reported by Slaton who had also observed no significant correlations between the stride time measures and the anthropometric measures or age variables, a finding substantiated by the present study. Many of the commonly used descriptors of gait have been found to be correlated with walking velocity. Although the walking velocity on day 1 (1.20 m/set) was not significantly different than on day 2 (1.19 m/set), for a given subject, the coefficient of variation values for the variability over trials ranged from 3 to 31%. This would indicate that for some subjects the velocity values did differ considerably from trial to trial. With the age range selected for study, it was not possible to control the walking velocity or to analyze only those trials that fell within a certain tolerance of a desired walking velocity. It was also decided that normalizing by walking velocity tended to produce artificial, less meaningful, measures. Differences between boys and girls were observed for the segmental center of gravity velocity values, notably the vertical velocity of the lower extremity segments at heel strike and the vertical velocity of the thigh and trunk at both heel strike and mid-swing. Subjectively, the boys tended to walk with a more ‘bouncy’ gait showing greater vertical displacement of the anatomical markers throughout the gait cycle. The significant differences in the vertical velocity measures may lend quantitative support to the visual observation of sex differences in the walking style. Comparison of the values obtained in the present study with previ-
478
N.L. Greer et al. / Children’s g-art
ous research is difficult as many of the studies did not report complete results. It is interesting to note that although their data was derived from children 6 years of age and older, Foley et al. (1979) reported similar standard deviation values and a similar pattern of lower values for the more proximal segments. The results of the relative and absolute angle and angular velocity calculations present many similarities. Significant differences between days were observed for the foot and ankle angles while few differences were noted between boys and girls for any of the angle measurements. Several significant correlations were observed between age and the relative angular velocity measures at the mid-swing point of the gait cycle. The negative correlation coefficients would indicate that the older children tended to have lower angular velocity values than did the younger children. A decrease in the angular velocity values associated with a segment may reflect the establishment of a smoother gait pattern. From the ground reaction force data, it is interesting to note the differences between the boys and girls and the relationship between the force values and the results of the kinematic analysis. The minimum vertical force occurs at approximately the point where the center of gravity of the body passes over the base of support. A lower minimum force value corresponds with greater knee flexion resulting in a lower center of gravity position. The results indicated that the boys had both a lower minimum force value and greater flexion of the knee at the mid-stance point. The relative time to the minimum force was longer for the boys than the girls. This would be expected as the knee angle was not different at the point of contact with the force platform but then became significantly less (more flexed) at the mid-stance point. There were no significant differences in the knee angular velocities at either the heel strike or mid-stance points. Based on a visual examination of the vertical ground reaction force curves, a ratio between the first and second maximum force values was determined. The ratio values were significantly different for the boys and girls (with a greater value for the boys). It is possible that this ratio may be reflective of the developmental stage of the gait pattern. Noguchi et al. (1985) reported higher vertical heel strike forces than push off forces although no distinction was made between boys and girls.
N. L. Grew et al. / Chddren’s gait
479
The point of transition from braking to propulsion (in an anteroposterior direction) occurred earlier in children than in adults. The expected transition point would be at approximately 50% of the stance phase while in the present study, the transition occurred at 37.7%. Noguchi et al. (1985) also reported an earlier transition point for children. The boys displayed a higher value for the medio-lateral force excursions variable. This variable reflects greater changes in the medio-lateral force between successive data samples. A higher value may indicate greater movement of the foot or of the total body over the foot and may also be reflective of a less developed gait pattern. Noguchi et al. (1985) had noted that the medio-lateral force pattern was the last of the three force components to mature. The results of the present study provide a description of the temporal and spatial, kinematic, and ground reaction force characteristics of the gait of 3- and 4-year-old children. The identification of differences between boys and girls represented a secondary question. When considering the results, it should be remembered that the large number of analyses completed may have contributed to a chance finding of significance. In addition, when the children were divided into sub-groups, the resulting sample sizes may have been insufficient to identify true differences between the groups. Nevertheless, it would appear that even at age 3 and 4, differences between boys and girls should be considered.
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